The present invention relates to an extrusion press. More particularly this invention concerns a residue stripper for such a press that forms metal into rods or bars.
In the direct extrusion of metal profiles, rods, and tubes from brass, aluminum, copper, lead, and the like a billet of the metal is inserted into a tubular guide or container whose front end is pressed against a back face of an extrusion die formed with a passage corresponding to the profile of the piece to be produced. A ram engaged into a rear end of the container forces the metal plastically through the die to produce the desired workpiece which is characterized by an extremely fine grain structure, smooth surface, and accurate shape.
The ram stops when its front end is at a short spacing from the back face of the die, leaving on the rear end of the extrusion a plug of residue. The container is retracted backward to expose this residue which must then be cut off the workpiece so it can be pulled out of the front end of the die.
According to German patent 553,782 the residue is sheared off the trailing end of the workpiece by a blade that is moved transversely across the back face of the die. If there is any misalignment between the residue-stripping blade and the die various problems can result. If the blade is too close it can gouge into and damage the die or get stuck on the die. If it is too far it can leave residue on the back face of the die, making it difficult to set the container flush on the die for the next extrusion operation and also making it difficult to get the workpiece out of the die assembly.
It is therefore an object of the present invention to provide an improved stripper assembly for a direct-extrusion press.
Another object is the provision of such an improved stripper assembly for a direct-extrusion press which overcomes the above-given disadvantages, that is which ensures clean removal of the residue from the back face of the die without damage to the die or lodging of the cutter on the workpiece.
According to the invention a stripper assembly used in combination with a metal-extrusion press having a die with a back face on which residue is formed during an extrusion operation, has a blade carrier moveable generally parallel to the die back face, a blade pivotal on the carrier and having an edge engageable with the die back face, and a biasing element braced between the blade and the carrier for urging the blade edge with a predetermined force transversely against the die back face.
Thus with this system the blade can compensate for minor movements of the die, caused for instance by thermal expansion, and will always cleanly remove the residue on its back face. It is possible to set the biasing force such that clean stripping is ensured without damage to the die assembly. If the blade encounters, for example, a hard crystalline deposit on the die back force, it will be able to deflect outward without damage to itself.
According to the invention the biasing element is a pack of spring washers. The blade has a back stripper face and the carrier has a confronting front stripper face. One of the stripper faces is formed with a pocket open toward the other of the stripper faces and holding the biasing element. Such a spring back can readily be set to produce any desired biasing force, even a relatively great one as is normally needed. The die back face can have a bevel on its edge turned toward the stripper assembly so that, when the blade is advanced into contact with the die back face, the blade is cammed back against the spring force.
The stripper assembly further has according to the invention a stop bolt threaded into the carrier, extending through the blade, and having a head engageable with a front face of the blade. Thus the outer position of the blade is defined by the bolt head which acts as a stop or abutment. During normal residue removal a space of about 1.5 mm is present between the bolt head and the blade.
A pusher member can be engaged between the blade and the carrier. Furthermore the pivot defines an axis and the carrier and blade have complementary semicylindrical surfaces centered on the axis and bearing on each other. Thus there is good force transmission via surface contact between the carrier and the blade.